The proposal, Force Balance in Polyelectrolyte Systems, can be considered to consist of two parallel, separate programs. One is to apply the model developed by Brenner and McQuarrie (1) to geometries other than the parallel cylinder-cylinder interaction considered by these authors. In this model, the polyelectrolyte is treated as a body with ionizable groups distributed uniformly over its surface, and the degree of ionization of these groups (say carboxyl groups) is allowed to respond to the local surface hydrogen ion concentration, which in turn depends upon the charge on the polyelectrolyte, or its degree of ionization. Thus we have a cyclic condition, which can be handled readily mathematically by what we call self-consistent boundary conditions. The second, parallel effort of the proposal is concerned with extending the range of ionic strength or concentration dependence of the above model. Since the model is based on the Debye-Huckel theory, it is necessarily restricted to very low salt concentrations, say less than 0.01 molar for a 1-1 electrolyte. This is the primary shortcoming of the model. Much work on classical colloid stability theory is based upon the non-linear Poisson-Boltzmann equation, but since this equation is not exact it is difficult to assess the validity of these theories even within the obvious deficiency in applying the classical theory to physiological or biological systems. In the past year we have made a thorough analysis of the validity and limitations of the non-linear Poisson-Boltzmann equation and have compared its predictions to those of some rigorous recent statistical mechanical theories. Bibliographic references: S.L. Brenner and D.A. McQuarrie, J. Theor. Biol. 39, 343 (1973); J. Coll. and Interface Sci. 44, 298 (1973); Biophys. J. 13, 301 (1973).